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Developing effective strategy to passivate surface defects in quantum dots (QDs) is critical to achieving high‐efficiency and long‐life perovskite light‐emitting diodes (LEDs). Here, the supramolecular interaction underpinning of organic‐inorganic components is exploited and a facile method is proposed to generate multiple‐hydrogen‐bonded supramolecular‐perovskite crystal structures on QD surfaces by introducing O‐Tolylbiguanide (O‐Tg) during QD synthesis, enabling bright, conductive, and water‐resistant CsPbI3 QDs. Compared with commonly used oleic acid and oleylamine ligands, the biguanide functional group in O‐Tg not only forms multiple hydrogen bond interactions with lead halide octahedra passivating both bridging‐ and terminal‐halogen ion defects, but also compatibly occupies the A‐site position stabilizing the crystal structure simultaneously. With fewer nonradiative defects and introduced hydrophobic benzene rings preventing eroding of polar molecules, CsPbI3 QDs exhibit remarkable photoluminescence quantum yields of 96%, and their film can be submerged in water for 30 h without degrading. The corresponding LEDs display a high external quantum efficiency (21.2%) and offer superior operational stability with a lifetime (T90) of 25 h at a constant current density as high as 50 mA cm−2. [ABSTRACT FROM AUTHOR]

Perovskite‐based light‐emitting diodes (PeLEDs) with a mixed halide composition can be used to obtain the "pure red" emission, i.e., in the 620–650 nm range, required for high‐definition displays. However, fast halide ion migration induces phase separation in these materials under electric fields, resulting in poor spectral stability and low efficiency. Herein, a method for producing mixed halide CsPbI3‐xBrx quantum dots (QDs) is reported in which ion migration is suppressed. The mixed halide composition is first achieved by anion exchange between CsPbI3 QDs and hydrobromic acid (HBr), during that the bromine ions efficiently passivate the iodine vacancies of the QDs. The original oleic acid ligands are then exchanged for 1‐dodecanethiol (1‐DT), which suppresses halide ion migration via the strong binding of the sulfhydryl group with the QD surface. PeLEDs based on these QDs exhibit a pure‐red electroluminescence (EL) peak at 637 nm, a maximum external quantum efficiency (EQE) of 21.8% with an average value of 20.4%, a peak luminance of 2653 cd m−2, and low EQE decease with increasing luminance. The EL spectrum of these devices is stable even at 6.7 V and they have an EQE half‐life of 70 min at an initial luminance of 150 cd m−2. [ABSTRACT FROM AUTHOR]

Colloidal perovskite nanocrystals (NCs) have risen rapidly in luminescence efficiency and color purity. However, their high performance requires careful and complex pre‐treatment of precursors and precise regulation of the reaction atmosphere; otherwise, their emission will be weak and broad. To overcome these limitations, we develop a facile ligand exchange method using a new type of bidentate ligand, which is obtained by reacting cheap sulfur with tributylphosphine (S‐TBP). During ligand exchange, the double bond between P and S atoms breaks and a single bond is formed between them, after which S‐TBP switches into a bidentate ligand and binds to a perovskite NC at two points. With short‐chain S‐TBP ligands that have high spatial position resistance, both NC spacing and surface ligand density can be reduced, thereby improving carrier injection and transport. On the NC surface after ligand exchange, halogen vacancies were substantially filled, leading to a PbSP (Pb, S, and P elements) component‐dominated shell that greatly decreases trap density and enhances material stability. The resulting perovskite NCs are stable and bright with a photoluminescence quantum yield of ≈96 %, and an external quantum efficiency of 22 %. Note that our ligand‐exchange strategy remains effective even when scaling up, which should accelerate commercialization. [ABSTRACT FROM AUTHOR]

Developing the technology for high yielding photocatalytic hydrogen evolution reactions is an important challenge. Development and optimization of photocatalytic junctions is a likely route for achieving this if heterojunctions with suitable band alignments can be achieved in sufficiently high‐density form. Here, a novel anatase‐TiO2/H‐rutile‐TiO2 heterophase homojunction system with near optimum energy band alignment is reported. The resulting as‐prepared catalyst exhibits an excellent photocatalytic hydrogen evolution rate of 29.63 mmol g–1 h–1 under UV–vis light irradiation and an outstanding apparent quantum efficiency of 45.6% at 365 nm. The significant improvement is ascribed to near perfect lattice matching in combination with the rapid separation and transfer of photogenerated carriers in anatase‐TiO2/H‐rutile‐TiO2 heterophase homojunctions. In situ X‐ray photoelectron spectroscopy, electron spin resonance spin‐trapping tests, femtosecond transient absorption spectroscopy, steady‐state surface photovoltage spectroscopy, and transient‐state surface photovoltage with additional ex situ characterizations and theoretical calculations show that the mechanism is enhanced transfer of photogenerated carriers in the anatase‐TiO2/H‐rutile‐TiO2 catalyst. This work provides a pathway for enhancing photocatalytic performance through optimization of heterojunctions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pyridine conjugated graphitic carbon nitride is successfully synthesized. • As-prepared catalyst exhibits superior photocatalytic hydrogen evolution. • Modulated localization of electron cloud density in as-prepared catalyst. • Narrowed bandgap and enhanced carriers' separation efficiency in as-prepared catalyst. High photogenerated carrier recombination and poor visible light response in symmetry graphitic carbon nitride are two classical problems for photocatalytic hydrogen evolution. In this work, we rationally design a novel carbon nitride (DPCN) with asymmetric embeddedness of pyridine ring. The embedded pyridine ring modulates the localization of electron cloud density, resulting in a narrowed bandgap and an enhanced carriers' separation efficiency. They are further confirmed by UV–vis spectra and femtosecond transient absorption (fs-TA) spectroscopy, whose results are consistent with DFT theoretical calculations. This DPCN catalyst shows enhanced photocatalytic hydrogen evolution rate of 180.5 μmol h−1 and the apparent quantum efficiency of 14.6 % at 420 nm, surpassing most reported g-C 3 N 4 -based photocatalysts. This work provides a new sight on designing two-dimensional photocatalysts by modulating the localization of electron cloud density through breaking topological symmetry. [ABSTRACT FROM AUTHOR]